Forged flange cylinder liner and method of manufacture

ABSTRACT

A cylinder liner is formed from a cylinder liner blank which includes a cylinder liner body having cylindrical sidewalls which define an internal diameter, an external diameter and a cylindrical lower extent. The cylinder liner blank is formed from a class of carbon alloy steels. A manufacturing method is shown for providing the cylinder liner blank with a flanged region at an upper extent of the cylindrical body by utilizing a cold forging process.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to cylinder liners for internalcombustion engines, particularly diesel engines, and to a method formanufacturing a cylinder liner blank.

2. Description of the Prior Art

There is a continuing demand in internal combustion engine technologyfor increased horsepower and performance from such engines.Additionally, in order to meet environmental requirements for reducedemissions, internal combustion engines, including diesel engines, arebeing designed to operate at higher compression pressures andtemperatures. Unfortunately, a direct correlation exists between thehigher compression pressures and temperatures and heat production by theengine with a consequent increase in stress on the engine internalcomponents. As a result of such factors as these, an upgrade of theengine block and associated components maybe required. Such componentsinclude the “cylinder liners” which are the subject of the presentinvention.

Conventional diesel engines have replaceable cylinder liners of theflange-type which are inserted into the engine cylinder. Such sleevesfacilitate machining and finishing on both the internal diameter and theouter diameter of the liner, which machining and finishing would be muchmore difficult to perform on the engine block itself. Cylinder linersalso offer an advantage when the engine is rebuilt, since the liner canbe replaced much more economically than the block.

The finished cylinder liner profile includes a flange or lip around oneend where it seats on the face of the engine block. The finishedcylinder liners are machined at the present time from stock called linerblanks. To avoid having to machine a significant thickness of materialfrom virtually the entire OD length of the liner blank, the design callsfor a thickened area to be formed onto the blank.

Typical industry practice for diesel engines is to use liners made fromgray cast iron that includes the flange feature cast at the end of theliner blank.

In the manufacturing processes using gray cast iron, a thick cylinder istypically prepared of cast iron by a centrifugal casting method. Thecasting forms the cylinder sidewalls as well as a flange portion on theouter circumferential region at one end of the casting. However, thesecast liners are not generally capable of withstanding the stressesinduced by the operational conditions (increased pressures andtemperatures) present in the latest generation of engine design, asdiscussed above.

One way to address this weakness is to require that the cylinder linersbe made from steel, rather than from cast iron. Different techniqueshave been proposed in the past for producing a cylinder liner blank froma steel tube, including the thickened area for the flange. One prior arttechnique utilized a steel pipe with the flange portion of thecylindrical tube being formed by folding one end of the tube outward. Ashortcoming of this technique is that the width of the flange wallcannot be enlarged because the flange wall is formed by folding thecylinder outward. Generally speaking, the thickness is smaller at theflange wall than at the cylindrical tube body so that the flange wallhas a tendency to have an insufficient mechanical strength at the pointof formation of the flange. In some cases, the flange wall strengthobtained is insufficient due to fine cracking about the circumference atthe point of the fold or roll. Also, the cylindrical tube is liable tobe bent inward at the folded portion or in the vicinity thereof.

It has been suggested that a hot forging technique be devised forproducing an upset on the cylinder liner blank to create the flange.However, as will be seen in the description of the invention whichfollows, it has been found particularly advantageous to utilize aforging process in which the forging is done with the metal in the coldcondition, as opposed to upsetting using a hot forging process.

A need exists for a method for manufacturing a cylinder liner blank ofthe type used to form a cylinder liner for an internal combustion enginewhich cylinder liner meets and exceeds the requirements for today'sincreased temperature and compression requirements.

A need also exists for such a manufacturing method which produces acylinder liner blank from a carbon steel alloy which liner is forged ina cold forging process.

A need also exists for an improved cylinder liner blank which isproduced by the aforesaid cold forging process as will be described.

SUMMARY OF THE INVENTION

In the method of the present invention, an improved cylinder liner blankis provided for an internal combustion engine, particularly a dieselengine, in which a cold forging process is utilized to form the flangedregion of the sidewall of the cylinder liner blank. The method ofmanufacture of the invention is used to produce a cylinder liner for aninternal combustion engine including a cylinder block having at leastone cylinder bore. In the first step of the invention, a cylindricaltube is produced from a carbon alloy steel. The cylindrical tube hasgenerally cylindrical sidewalls, an internal diameter and an externaldiameter, and an overall length based upon predetermined startingdimensions as dictated by the end application for the cylinder blank.

The cylindrical tube is cut or otherwise dimensioned to the startingdimensions of the unforged cylinder liner blank. The unforged cylinderliner blank is placed into a hydraulic press and cold formed into aforged cylinder liner blank. The cylinder liner blank includes a linerbody with cylindrical sidewalls which define an internal diameter, anexternal diameter, a cylindrical lower extent and a flanged or upsetregion at an upper extent thereof which is integrally formed in the coldforging process. The flanged region of the cylinder liner blank extendsradially outwardly relative to the external diameter of the cylindricalsidewalls of the cylinder body so as to define a stop shoulder, the stopshoulder being cooperatively received in abutting relation to a matingsurface defined by the cylinder bore of the internal combustion engine.

Preferably, the cylinder blank is formed from a carbon alloy steelhaving a carbon content of at least about 0.25%, more preferably greaterthan about 0.50%. In a particularly preferred embodiment of theinvention illustrated herein, the cylinder blank is formed of 1055carbon alloy steel. The forged cylinder blank has an internal diameterin the range from about 3 to 8 inches in most cases.

In a particularly preferred method of the invention, the unforgedcylinder liner blank is placed into a forging die of a hydraulic press.The hydraulic press has a forging die with a die cavity for receivingthe cylinder liner blank and an upper, flange cavity of greater relativediameter than the die cavity. A closely fitting forming mandrel isreceived within the internal diameter of the cylinder liner blank withinthe forging die. A hydraulic force is then applied to the unforgedcylinder liner blank in the forging die by means of a forging die cap tothereby cold form an integral flanged region on the cylindricalsidewalls of the cylinder blank at an upper extent thereof. The coldforging step includes applying anywhere from about 500 to 1,000 tons ofhydraulic force to the cylinder liner blank to cause the carbon alloysteel to flow into the flange cavity to form the flanged region of thecylinder body.

A method of assembling an internal combustion engine is also described,the engine having a cylinder block and at least one cylinder bore. Inthe method of assembly, a forged cylinder liner blank of the typedescribed is first machined to a finished state to form the finishedcylinder liner. The finished cylinder liner is then concentricallydisposed at a location within the cylinder bore and secured to thecylinder block. The flanged region of the cylinder liner so formedextends radially outwardly relative to the external diameter of thecylindrical sidewalls of the cylinder body so as to define a stopshoulder, the stop shoulder being cooperatively received in abuttingrelation to a mating surface defined by the cylinder bore of theinternal combustion engine.

Additional objects, features and advantages will be apparent in thewritten description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified, side sectional view of the hydraulic press anddie set used to cold forge the cylinder liner of the invention.

FIG. 2 is partial sectional view of a portion of the die set of FIG. 1,showing the flange forming step of the invention.

FIG. 3 is an isolated view of a longitudinal section of the cylinderliner of the invention showing the relative hardness values for variousregions of the cylinder liner blank after cold forging.

FIG. 4 is a picture of the grain flow taken from a slice of a cylinderliner blank made according to the method of the present invention.

FIG. 5 is a photograph at 100× of the microstructure of the straightcylinder area of the liner blank of FIG. 4.

FIG. 6 is a view similar to FIG. 5 at 100× of the forged, flange area ofthe cylinder liner blank.

FIG. 7 is a partial, cross sectional view of a typical prior artfinished cylinder liner for a diesel engine.

FIG. 8 is a side, cross sectional view of an exemplary cylinder linerblank for a diesel engine showing the relative dimensional relationshipsthereof.

DETAILED DESCRIPTION OF THE INVENTION

Turning first to FIG. 7, there is shown a prior art diesel enginecylinder arrangement for an internal combustion engine. The pistoncylinder shown in FIG. 7 is typical of the prior art and is intended toexplain the general environment of the present invention. The powercylinder 10 shown in FIG. 7 is part of a conventional (and thus notillustrated) diesel engine. Such engines usually have a cylinder borediameter in the range from about 3 to 8 inches.

The power cylinder 10 is received within the block 12 of the engine andincludes a cylinder liner 11 of the type under consideration in thediscussion which follows. The liner 11 slidably receives the pistonassembly 15 which may vary in construction, depending upon the type ofvehicle, pump, or engine under consideration. The upper extent of thecylinder liner 11 is enclosed by a conventional cylinder head 16 securedagainst the liner and block and sealed by a head gasket 17 to define,with the upper side of the piston assembly 15, a combustion chamber 19.The piston assembly 15 is connected in the usual manner to the enginecrankshaft (not shown), as by connecting rod 20.

In the particular arrangement illustrated in FIG. 7, the piston assembly15 comprises a piston 21 of generally conventional design for dieselengines. The assembly includes a trunk type piston constructed of castor forged aluminum alloy having an insert 22 made of an impact resistantmaterial which is compatible to the aluminum alloy in its coefficient ofthermal expansion and other properties. A top ring groove 24 is machinedto receive a top compression ring 25 of the split annulus type. Beneaththe top ring groove 24, a second keystone-shaped ring groove 26 ismachined in the aluminum alloy piston body to receive the secondcompression ring 27 also of the split annulus type. Beneath the secondring groove 26, a third rectangular groove 28 is machined in thealuminum piston in which a conventional oil control ring 29 is received.As is conventional in the art, the piston 21 contains an internal cavity(not shown) conventionally cooled by an oil jet spray, from which thetop and second ring grooves 24 and 26 are isolated. The oil ring groove28 customarily has small holes drilled into the cavity to permit thedrainage of oil. Beneath the oil control ring groove 28, the pistoncomprises the customary skirt 30 for effecting the usual guiding fit ofthe piston with the walls of the cylinder 11. Although a trunk typepiston has been described it will be evident that the invention will beequally applicable to other type piston designs, as well. Thedescription of the piston assembly 15 is not intended to be limiting ofthe scope of the present invention, but is merely intended to explainthe operating environment of the cylinder liner 11.

The cylinder liner 11, shown in FIG. 7, is machined from a blank, asshown in FIG. 8, and includes a cylinder liner body having cylindricalsidewalls 31 which define an internal diameter 33 and an externaldiameter 35 for the liner body. The body also includes a cylindricallower extent 37 (shown broken away in FIG. 7) and an upper, flanged orupset region 39. The present inventive method is directed toward aprocess for providing the cylinder liner 11 with a flanged or upsetregion 39 in which a forging process, preferably a cold forging process,is applied to a class of carbon alloy steels. Although the invention isnot limited to particular cylinder liner dimensions, the prototypedimensions shown in FIG. 8 are as follows (all dimensions being ininches):

-   d1=5.26-   d2=6.39-   d3=6.73-   l1=10.93-   w1=0.598

The method of forming the cylinder liner blank of the invention will nowbe described, primarily with reference to FIGS. 1 and 2. In the firststep of the method, a cylindrical tube is formed from an alloy steel.The cylindrical tube can be formed in any convenient manner. Forexample, the cylindrical tube can be formed by machining a solid barstock of steel to provide a cylinder liner blank having the requiredstarting dimensions. Alternatively, a seamless carbon alloy steel tubecan be provided directly by the steel mill for use in the process of theinvention. The starting tube would then be cut to the desired size. Inthis case, for example, a 20 foot starting tube might be cut intoindividual tubes of approximately 10½ inches in length. The requiredstarting dimensions will depend upon the particular application,however. By way of example, the final dimensions of the cylinder linerabove may be used for comparison.

The unforged cylinder liner blank (41 in FIG. 1) is then placed withinthe forging die set 43 of a hydraulic press 45. The forging die set 43includes a forging die cavity 47 for receiving the unforged cylinderliner blank and has an upper flange cavity 49 of greater relativediameter than the die cavity. As shown in FIG. 1, a closely fittingforming mandrel 51 is received within the internal diameter 33 of theunforged cylinder liner blank.

In the next step of the method, hydraulic force is applied to theunforged cylinder liner blank in the die cavity by means of the forgingdie cap 53 to thereby cold form an integral flanged region (39 in FIG.2) on the cylindrical sidewalls of the cylinder liner blank at an upperextent thereof. As shown in FIG. 2, the flanged region 39 extendsradially outwardly relative to the external diameter of the cylindricalsidewalls of the cylinder body so as to define a stop shoulder (55 inFIG. 8). The forged cylinder liner blank would then receive any finalmachining of the type normally applied to cylinder liner blanks for theparticular engine application at hand in order to form the finishedcylinder liner. The stop shoulder 55 formed in the forging process iscooperatively received in abutting relation to a mating surface, such asan annular shoulder (61 in FIG. 7) defined by the cylinder bore of theinternal combustion engine. The upper extent of the cylinder liner isdimensioned so as to form a close interference fit (i.e. 0.0005 to0.0015 inch clearance) with the cylinder bore. The finished cylinderliner is secured in place by the cylinder head and head bolt clamp loadin a conventional manner when installed within a diesel engine.

Although a variety of starting materials can be utilized for thecylinder liner blank 41, the preferred materials for the diesel enginecylinder liners of the invention are carbon alloy steels. Preferably,the carbon alloy steels have a relatively high carbon content, generallygreater than about 0.25%, more preferably greater than about 0.50%. Themost preferred material for the particular application illustrated is a1055 carbon alloy steel having a carbon content of approximately 0.55%.

The hydraulic force applied by the press can range anywhere from about500 tons to 1,000 tons, depending upon the starting material andultimate dimensions of the finished product. Although the process is acold forging process and can be carried out without heating the cylinderliner blank, there may be applications in which the upper extent of thecylinder liner blank is heated, as by induction heating, in the range ofabout 1200° F. to reduce stress during the cold forging process tothereby increase the useful production life for the hydraulic die andforming mandrel.

The following example is intended to be illustrative of the inventionwithout limiting the scope thereof:

EXAMPLE I

A prototype run was conducted to determine the forging processparameters for a cylinder liner for diesel engine application. Theforged cylinder liner blank was produced by cold forging from a startingcylinder liner blank of 1055 carbon steel alloy using the previouslydescribed method steps. Testing was then performed to check for grainflow and for any folding back of material at formed area. No targethardness values were specified, but attention was given to anydifference in hardness at the formed area versus the non formed area ofthe cylinder liner. For the prototype run, a 3.500 inch externaldiameter bar was used.

Starting Material:

The original material was 3.5″OD solid bar stock, heat number D39421.The material was machined into a cylinder having an internal diameter of2.490 inches, an external diameter of 3.400 inches and an overall lengthof 3.000 inches.

Tooling:

The forging tool material was 4140 steel, heat treated to the hardnessrequired to deform the 1055 carbon alloy starting cylinder liner blank.

Process:

The process was a cold forging process performed on a hydraulic press.

Process Evaluation:

One of two parts made was cut and metallurgically evaluated. A grainflow slice was removed, polished, and macro etched to determine materialflow lines. A picture of the grain flow is presented in FIG. 4. Due toinsignificant amount of deformation and clean material, there were noobvious flow lines visible. The microstructure of the flanged insert isillustrated in FIGS. 5 and 6. Both the upset (flange) area, FIG. 6, andthe undeformed straight cylinder area, FIG. 5, were evaluated. Theflange area shows slightly elongated grains as compared to the straightcylinder area. The photomicrographs represent as-received material fromthe mill and no heat treatment was performed.

The hardness survey (FIG. 3) shows some difference between the flangedregion and the remaining undeformed cylinder. The slightly higher valuesin the flanged region are a result of the cold working during upsetting.

An invention has been provided with several advantages. The method ofmanufacture of the invention shows that carbon alloy starting blanks cansuccessfully be cold forged to create the flanged cylinder liners of theinvention. There are no visible forging defects such as laps, foldovers,or undesirable material flow. Slightly higher hardness values wereobserved in the flanged area due to cold upset, but no undesirableoverall effects were realized. The cold forged cylinder liners of theinvention, formed from carbon steel alloys, provide the structuralintegrity needed for many of today's internal combustion engines whichoperate at higher compression temperatures and pressures. Themanufacturing process is simple to implement and economical to carryout.

While the invention has been shown in only one of its forms, it is notthus limited but is susceptible to various changes and modificationswithout departing from the spirit thereof.

1. A method of manufacturing a cylinder liner blank for an internalcombustion engine including a cylinder block having at least onecylinder bore, the method comprising the steps of: providing acylindrical tube of predetermined dimensions which is formed from acarbon alloy steel starting material; placing the cylindrical tube intoa hydraulic press and cold forging the cylindrical tube into a cylinderliner blank, the cylinder liner blank comprising a liner body withcylindrical sidewalls which define an internal diameter, an externaldiameter, a cylindrical lower extent and an upper flanged region whichis integrally formed in the cold forging process.
 2. The method of claim1, wherein the flanged region of the cylinder liner blank extendsradially outwardly relative to the external diameter of the cylindricalsidewalls of the cylinder body so as to define a stop shoulder, the stopshoulder being cooperatively received in abutting relation to a matingsurface defined by the cylinder bore of the internal combustion engine.3. The method of claim 3, wherein the cylinder liner blank is formedfrom a carbon alloy steel having a carbon content of at least about0.25%.
 4. The method of claim 3, wherein the cylinder liner blank isformed from a carbon alloy steel having a carbon content of at leastabout 0.50%.
 5. The method of claim 3, wherein the cylinder liner blankif formed from a 1055 carbon alloy steel.
 6. The method of claim 3,wherein the cylinder liner blank has an internal diameter in the rangefrom about 3 to 8 inches.
 7. A method of manufacturing a cylinder linerfor a diesel engine including a cylinder block having at least onecylinder bore, the method comprising the steps of: providing acylindrical tube which is formed from a carbon alloy steel startingmaterial and dimensioning the cylindrical tube to form an unforgedcylinder liner blank of predetermined starting dimensions; placing theunforged cylinder liner blank into a hydraulic press, the hydraulicpress having a forging die set with a die cavity for receiving theunforged cylinder liner blank and an upper, flange cavity of greaterrelative diameter than the die cavity; closely fitting a forming mandrelwithin the internal diameter of the cylinder liner blank within theforging die set; applying a hydraulic force to the cylinder liner blankin the forging die set to thereby cold form an integral flanged regionon the cylindrical sidewalls of the cylinder liner blank at an upperextent thereof; and finish machining the forged cylinder liner blank toform a cylinder liner.
 8. The method of claim 6, wherein the flangedregion of the cylinder liner extends radially outwardly relative to theexternal diameter of the cylindrical sidewalls of the cylinder body soas to define a stop shoulder, the stop shoulder being cooperativelyreceived in abutting relation to a mating surface defined by thecylinder bore of the internal combustion engine.
 9. The method of claim7, wherein the cylinder liner blank is formed from a carbon alloy steelhaving a carbon content of at least about 0.25%.
 10. The method of claim7, wherein the cylinder liner blank is formed form a carbon alloy steelhaving a carbon content of at least about 0.50%.
 11. The method of claim7, wherein the cylinder liner blank if formed from a 1055 carbon alloysteel.
 12. The method of claim 7, wherein the cold forging step includesapplying 500 to 1,000 tons of hydraulic force to the cylinder linerblank to cause the carbon alloy steel to flow into the flange cavity toform the flanged region of the cylinder body.
 13. The method of claim 7,wherein the upper extent of the cylinder liner blank is heated withinduction heating in the range of about 1200° F. to reduce stress duringthe cold forging process and enable an increased production life for thehydraulic die set and forming mandrel.
 14. A method of assembling aninternal combustion engine having a cylinder block and at least onecylinder bore, the method comprising the steps of: locating a cylinderliner in a concentrically disposed location within the cylinder bore andsecured to the cylinder block, the cylinder liner being prepared in amanufacturing process by: providing a cylindrical tube formed fromcarbon alloy steel of predetermined starting dimensions; dimensioningthe cylindrical tube to form an unforged cylinder liner blank; placingthe cylinder liner blank into a hydraulic press and cold forming thecylinder liner blank into a forged cylinder liner blank, the forgedcylinder liner blank comprising a liner body with cylindrical sidewallswhich define an internal diameter, an external diameter, a cylindricallower extent and an upper flanged or upset region which is integrallyformed in the cold forging process; finish machining the forged cylinderliner blank to form a finished cylinder liner; and wherein the flangedregion of the finished cylinder liner extends radially outwardlyrelative to the external diameter of the cylindrical sidewalls of thecylinder body so as to define a stop shoulder, the stop shoulder beingcooperatively received in abutting relation to a mating shoulder definedby the cylinder bore of the internal combustion engine.
 15. The methodof claim 14, wherein the internal combustion engine is a diesel engineand wherein the cylinder body has an internal diameter in the range fromabout 3 to 8 inches.
 16. The method of claim 14, wherein the cylinderliner blank is a carbon alloy steel having a carbon content of at leastabout 0.50%.
 17. The method of claim 16, wherein the cylinder linerblank is formed of 1055 carbon alloy steel.